Hold Still, Butterflies. Britain Is Counting.

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A butterfly at London Zoo last month. Three-quarters of the 56 species of butterflies in Britain and Ireland are in decline, according to the charity Butterfly Conservation.CreditCreditToby Melville/Reuters

LONDON — To gauge the health of the environment, look to the butterfly.

The delicate, colorful insects that help to pollinate many an English garden may not live very long (the monarch butterfly has a life span of two to six weeks), but knowing how well their colonies are faring and how many are flitting around can be crucial indicators of a calamitous or a thriving environment.

The call has gone out for legions of volunteers to join the campaign, which runs from Friday to Aug. 12, and submit their sightings of butterflies and day-flying moths.

The effort, called the world’s biggest butterfly survey, has the backing of the British broadcaster and naturalist David Attenborough, who is also the president of Butterfly Conservation, the charity that organizes the effort. Mr. Attenborough told the BBC that watching butterflies in his garden takes his mind off “the woes of Brexit,” referring to Britain’s contentious exit from the European Union.

The survey began in 2010, and last year, a record 60,000 people turned in 62,500 counts of butterflies and day-flying moths from across the United Kingdom, according to Butterfly Conservation, which describes the effort as the largest butterfly count in the world.

Volunteers in the big count need spend only 15 minutes in a garden, park or wood counting butterflies and moths before submitting their figures to help chart the insects’ abundance. The campaign provides a chart to turn in information, and free iOS and Android apps to record the data.

Britain’s butterflies may not be so lucky. A 2015 report noted “evidence of the serious, long-term and ongoing decline of U.K. butterflies,” with 70 percent of species declining in occurrence and 57 percent declining in abundance since 1976, Butterfly Conservation says.

Four butterflies have become extinct in the past 150 years, scientists say, and three-quarters of the 56 species of butterflies in Britain and Ireland are in decline, according to the charity, which says they have been under siege from “unprecedented environmental change.”

“Habitats have been destroyed on a massive scale, and now patterns of climate and weather are shifting unpredictably in response to pollution of the atmosphere, but the disappearance of these beautiful creatures is more serious than just a loss of color in the countryside,” the charity’s website says.

Apart from the insects’ intrinsic and economic value, the British government see butterflies and moths as important “indicators of biodiversity,” the organization says, adding, “Their fragility makes them quick to react to change so their struggle to survive is a serious warning about our environment.”

In 2017, the gatekeeper butterfly was the most commonly counted. The species expected to do well in this year’s survey include the holly blue, common white, common blue and red admirals.